1. Field of the Invention
The invention relates to a drawing pattern verifying method for verifying a drawing pattern of a mask for drawing a circuit pattern as a set of fine patterns of a semiconductor device and, more particularly, to a drawing pattern verifying method by use of partial or overall batch transfer employing a stencil mask.
The present application claims priority of Japanese Patent Application No. Hei11-323382 filed on Nov. 12, 1999, which is hereby incorporated by reference.
2. Description of the Related Art
There is put to practical use such a micro-lithography technology that, in steps of manufacturing semiconductor devices, utilizes a focused beam of such a charged particle beam as an electron beam (EB), ion beam, or a like, in order to draw integrated circuit patterns. For example, by one of such technologies, a relevant electron beam exposure apparatus applies the electron beam to a wafer coated with an electron beam-sensitive resist to directly project integrated circuit patterns to the wafer, by using an EB mask in order to obtain a required drawing pattern by use of the electron beam. Such an electron beam drawing technology by use of the electron beam comes in a partial batch exposure method or an overall batch exposure method, by either of which a mask pattern is reduced and projected to a give batch drawing of unit regions such as a memory cell. These two methods both use two masks usually, to shape the electron beam into a rectangular one by using a first mask and then apply this rectangular electron beam to a second mask. The second mask previously has a plurality of rectangular cell apertures on which is formed a partial pattern cut out of a drawing pattern to be projected to a wafer, so that these cell apertures are reduced several ten-fold through an electric optical system and then transferred to the wafer in batch exposure. These partial and overall batch exposure methods are superior to the variable shaped beam approach not only in a respect of an improved throughput due to a decrease in a number of projections required but also in a respect of such improvements in inter-projection connecting accuracy, slant pattern image quality, and pattern data compressibility that, for example, may have no direct influences on wafer drawing time even with finer patterning.
In addition, there is available as a lithography apparatus employing the ion beam such the ion beam transfer exposure apparatus, by which the mask pattern is projected in transfer to the wafer using the ion beam like the electron beam lithography apparatus. This method can provide batch projection of all chip patterns in transfer by using the ion beam to realize a higher throughput while maintaining a high resolution of ion beam exposure. This ion beam transfer method comes in such an approach that arranges the mask with patterns formed thereon near the wafer to thereby apply a large-diameter ion beam to the mask so that the transmitted ion beam may transfer these patterns or a reduction-projecting exposure approach that applies the ion beam to a five-fold or ten-fold sized mask to thereby perform reduction-projecting exposure of patterns onto the wafer.
The above-mentioned electron beam drawing technology uses two types of masks in batch exposure whereby circuit patterns are collectively projected to the wafer: a stencil mask having holes therein through which the electron beam passes to draw circuit patterns and a membrane type mask having a membrane for blocking the electron beam to do so.
In the case of the stencil mask, any region surrounded entirely by mask holes cannot have a portion thereof to support itself, so that such the stencil mask cannot be manufactured, which is hereinafter referred to as a donut problem. On the other hand, in a region surrounded largely by mask holes except a slight peripheral supporting portion thereof, as the portion entirely surrounded by the mask holes is much larger than the supporting portion, the slight peripheral supporting portion has a lower strength, so that when the transfer mask is made, this inner portion may be warped or deformed, which is hereinafter called a leaf problem. With this, to avoid such the donut problem and the leaf problem during manufacturing of transfer masks for drawing patterns, the mask must be checked to detect such problems manually or by use of pattern continuity so that any regions having thus detected problems may undergo application of the membrane type mask or division of patterns.
Manual detection, however, suffers from a problem of possibly creating large-scale pattern defects due to human error. The method of detecting isolated patterns by checking pattern continuity, on the other hand, suffers from a problem that it can detect only such regions that have the donut problem, so that it needs to use a separate program for the leaf problem.
In view of the above, it is an object of the invention to provide a drawing pattern verifying method for verifying drawing patterns created on a stencil mask that can use a same algorithm to detect patterns suffering from a donut problem or a leaf problem.
According to an aspect of the present invention, there is provided a drawing pattern verifying method for verifying a drawing pattern to be formed on a stencil mask used in electron beam exposure or ion beam exposure, including steps of:
extracting the drawing pattern from device designing data;
dividing a region in which the extracted drawing pattern is arranged except mask holes into a plurality of portions;
setting to each of divided portions a variable of a plurality of kinds of variables which are determined based on likelihood of defectiveness of the portions; and
reviewing a specific variable of the portion based on likelihood of defectiveness thereof.
With the foregoing aspect, since the region except mask holes providing openings in an area for arranging the drawing pattern therein is divided into a plurality of portions so that each of these divided portions may have the variable set thereto based on its own defect occurrence likelihood, such the portion that has the specific variable which is set finally thereto when these variables are reviewed can be identified to be a defective portion, thus previously detecting the region subject to pattern defect occurrence.
In the foregoing aspect, a first preferable mode is one wherein the reviewing step includes steps of:
further dividing the portion with the specific variable into the plurality of portions; and
setting to each of the portions the variable which is determined based on likelihood of defectiveness thereof; and the further dividing step and the setting step are repeated once or a plurality of times.
With the first preferable mode, if the portion of the specific variable cannot be specified as a pattern occurrence portion when it is reviewed, the variable can be reset to verify even more complicated drawing patterns of the portion.
Also, a second preferable mode is one wherein the portion of a finally set specific variable is a first defective portion entirely surrounded by mask holes and/or a second defective portion partially surrounded by mask holes.
With the second preferable mode, it is possible to extract both the first defective portion which provides the donut problem and the second defective portion which provides the leaf problem, by using a same algorithm.
Also, a third preferable mode is one wherein the variable setting step specifically sets variables a={a0}, {a1}, {a2} (where, a0‡a1‡a2) according to rules, the rules including:
a first rule for setting to a third portion an inner portion surrounded by straight lines which are in contact with the mask hole nearest to the region arranged in the drawing pattern and which are parallel with sides of the region and also setting an outside of the third portion to variable {0}, mask holes to variable {a2}, and remaining to variable {a1};
a second rule for performing first scanning on the region in X-axis and Y-axis directions, to set to variable {a0} such a portion of the variable {a1} that becomes of any selected one of variable permutations of {a0}xe2x86x92{a1}xe2x86x92{a2}, {a2}xe2x86x92{a1}xe2x86x92{a0}, and {a0}xe2x86x92{a1}xe2x86x92{a0} observed in the portion of the variable {a1} and adjoining both-side portions thereof as a result of scanning in both directions; and
a third rule for performing second scanning on the region in X-axis and Y-axis directions, to set to variable {a0} such a portion of variable {a1} that becomes of a variable permutation of {a0}xe2x86x92{a1}xe2x86x92{a0} observed in the portion of variable {a1} and adjoining both-side portions thereof as a result scanning in one or both of X-axis and Y-axis directions, and then performing third scanning in X-axis and Y-axis directions for setting in a same way as the second scanning; and
the specific variable is {a1}.
Also, a fourth preferable mode is one wherein the variable setting step specifically sets variables a={a0}, {a1}, {a2} (where, a0‡a1‡a2) according to rules, the rules including:
a fifth rule for setting sides of a region in which the drawing pattern is arranged to variable {a0}, mask holes to variable {a2}, and remaining to variable {a1};
the second rule 2 for performing first scanning on the region in X-axis and Y-axis directions, to set to variable {a0} such the portion of the variable {a1} that becomes any selected one of variable permutations of {a0}xe2x86x92{a1}xe2x86x92{a2}, {a2}xe2x86x92{a1}xe2x86x92{a0}, and {a0}xe2x86x92{a1}xe2x86x92{a0} observed in the portion of the variable {a1} and adjoining both-side portions thereof as a result of scanning in both directions; and
the third rule for performing second scanning on the region in X-axis and Y-axis directions, to set to variable {a0} such the portion of the variable {a1} that becomes of a variable permutation of {a0}xe2x86x92{a1}xe2x86x92{a0} observed in the portion of the variable {a1} and adjoining both-side portions thereof as result of scanning in one or both of X-axis and Y-axis directions, and then performing third scanning in X-axis and Y-axis directions for setting variables in the same way as the second scanning; and
the specific variable is {a1}.
Also, a fifth preferable mode is one wherein the rules further includes:
a fourth rule for, after the third rule is applied, performing final scanning in X-axis and Y-axis directions, to detect as the first defective portion such a portion of variable {a1} that becomes of a variable permutation of {a2}xe2x86x92{a1}xe2x86x92{a2} observed in the portion of variable {a1} and adjoining both-side portions thereof as result of scanning in both x-axis and y-axis directions and to detect as the second defective portion such the portion of variable {a1} that becomes of a variable permutation of {a2}xe2x86x92{a1}xe2x86x92{a2}, observed in the portion of variable {a1} and adjoining both-side portions, as result of scanning in either one of X-axis and Y-axis directions and of {a0}xe2x86x92{a1}xe2x86x92{a2} or {a2}xe2x86x92{a1}xe2x86x92{a0} as result of scanning in the other direction, thus detecting the portion of variable {a1} as the first defective portion or the second defective portion.
With the fifth preferable mode, it is possible to extract not only the donut problem or leaf problem occurrence region but also such the portion that only its mutually facing two sides are in contact with mask holes but other two sides not in contact with the mask hole are too short to support this variable {a1} portion so that it may give rise to a defect during the manufacturing of the stencil mask.
Also, a sixth preferable mode is one wherein when an aspect ratio of the second defective portion is smaller than a first threshold value, variable a of the second defective portion is reset from {a1} to {a0}.
With the sixth preferable mode, even if a shape is not clear beforehand that gives rise to the leaf problem, the first threshold value can be provided to thereby make setting arbitrarily whether a relevant portion is to be extracted as the leaf problem occurrence portion or not.
Also, a seventh preferable mode is one wherein the aspect ratio of the second defective portion is a magnitude of L2/L1, where L1 represents a length of such a side of the second defective portion that is in contact with a portion of variable {a0} and L2 represents a distance between a straight line passing through the side and a contact point, which is most distant in a direction perpendicular to the straight line, of the second defective portion and the portion of variable {a2}.
Also, an eighth preferable mode is one wherein by the second and third rules, the portion of variable {a1} which becomes of a variable permutation of {a0}xe2x86x92{a1}xe2x86x92{a0}, observed in the portion of variable {a1} and adjoining both-side portions thereof, as result of scanning in either of X-axis and Y-axis directions and of a variable permutation of {a0}xe2x86x92{a1}xe2x86x92{a2} as result of scanning in the other direction remains as of variable {a1} and is detected as a fourth defective portion if a value of L4/L3 is larger than a second threshold value, where L4 represents a length of a side of the portion of variable {a1} that is in contact with variable {a2} and L3 represents a length of a side of the portion of variable {a1} that is in contact with variable {a2}.
Also, a ninth preferable mode is one wherein the variable setting step specifically sets variables a={a0}, {a1}, {a2} (where, a0‡a1‡a2) according to rules, the rules including:
The first rule for setting to a third portion such a portion that is surrounded by straight lines which are in contact with a mask hole nearest to a side of a region in which the drawing pattern is arranged and which are parallel with sides of the region and also setting a portion outside the third portion to variable {a0}, mask holes to variable {a2}, and the remaining to variable {a1};
a sexth rule for extracting the portion of variable {a1} which is in contact with the portion of variable {a0} and which contains a single portion of variable {a2};
a seventh rule for forming a graphic which is in contact with a side of the portion of variable {a2} and which has a predetermined width, thus setting a variable for the graphic; and
an eighth rule for dividing variables of the extracted portion of variable {a1} based on the graphic, thus setting variables; and
the specific variable is {a1}.
With the ninth preferable mode, since the graphic can be formed along the side of the mask hole and set to the variable, the region in which the drawing pattern is arranged becomes rectangular typically, so that even when the drawing pattern is complicated due to, for example, oblique arrangement with respect to that side, the defective portion can be verified and extracted.
Also, a tenth preferable mode is one wherein the sixth, seventh and eighth rules are performed as many as number of variable {a2} provided.
Also, an eleventh preferable mode is one wherein the graphic formed according to the seventh rule is specifically formed in a priority order of a first graphic which is in contact with the portion of variable {a2}, which has a predetermined width, and which has opposite ends thereof in contact with the portion of variable {a0}, a second graphic which is in contact with a side of the portion of variable {a2}, which has a predetermined width, and which has one end thereof in contact with the portion of variable {a0} and the other end thereof in contact with the first graphic, and a third graphic which is in contact with a side of the portion of variable {a2}, which has a predetermined width, and which has opposite ends thereof in contact with the first graphic or the second graphic.
Also, a twelfth preferable mode is one wherein the first through third graphics formed are only such graphics that are in contact with a side of the portion of variable {a2} without a corner thereof or that are in contact with a side of the portion of variable {a2} with one corner thereof, the graphics without a corner thereof having priority over the graphics with a corner in formation.
Also, a thirteenth preferable mode is one wherein an angle of the corner of the first through third graphics with respect to the portion of variable {a2} is less than 270xc2x0.
With the thirteenth preferable mode, even a triangular region which has its two sides sandwiched by mask holes can be extracted as the defect occurrence portion.
Also, a fourteenth preferable mode is one wherein that further including a ninth rule for detecting the portion of variable {a1} which is in contact with none of the first through third graphics as a fifth region and the portion of variable {a1} which is in contact with any one of the first through third graphics as a sixth region, thus detecting portions of variable {a1} as the fifth portion or the sixth portion.
Also, a fifteenth preferable mode is one wherein the variable {a1} is reset to the variable {a0} if aspect ratio of the sixth portion is less than the third threshold value.
Also, a sixteenth preferable mode is one wherein the aspect ratio of the sixth portion is given as L6/L5, where L5 represents a length of a side of the sixth portion which is in contact with any one of the first to third graphics and L6 represents a length of a distance between a straight line passing through the side and a contact point, which is the most distance from the straight line in a direction perpendicular thereto, of the portion of variable {a1} and the portion of variable {a2}.
With configuration of the above, it is capable of detecting those portions to which the specific variables are set finally as a donut problem or leaf problem occurrence site beforehand, to perform special processing on masks having such a drawing pattern thereon, thus forming patterns in a stable manner.
Although the device pattern may come in a variety of kinds of patterns and it is extremely difficult to detect donut problem or leaf problem occurrence sites by visual inspection, with applying rules of setting variables, it is capable of simultaneously detecting the donut problem and leaf problem occurrence sites by using a single processing algorithm, and grasping the leaf problem occurrence sites. In addition, it is capable of assuming the leaf problem occurrence sites, based on a threshold value set in advance.